The Isis Adventure

I've sent this question in to Sonic Games, but am curious if anyone else has a similar puzzle - 1 of the 4 wheels sits flush with the puzzle body, whereas the other 3 are sunken in and spring-loaded. I figured the wheel was just a red herring, but tonight, I noticed it lifted a bit and was able to remove the wheel. There was a spring in there, along with a ball bearing to "click" the wheel when turning, but as it was lifted higher than the others, the bearing never clicked. The wheel has a pin on its axle along with a barb, and in the hole sits 3 hooks for the barb. However, no matter how hard I push the wheel, the barb won't go past the hooks to lock into place. There's an allen wrench socket at the bottom that the pin should fit into, but the wheel won't move it, so I suspect that's why I haven't had any luck opening the puzzle. Anyone else have a Tessarisis like this?

Which wheel?

Maybe I have the same issue!

All my wheels are spring loaded, to vaying degrees all flush with the surface and none seem to have a ball bearing to make them click .

I had difficulties with one wheel (the one which is next to but lower than the plunger when the puzzle is sitting on the cut off corner). It sometimes got "sticky" and would not push in or pop out or turn (but I think this only started after I had been pressing and turning for ages). Didn't do my finger any good at all, but it didn't always "stick" so I was still able to solve it (when it was unstuck) .

Sounds like yours had a different (real) problem however (

That needs to go back for repair none of the wheels should come out of the puzzle. Did you pull it out? or did it just fall out?

It's the wheel to the right of the plunger, and when I say "flush", I mean it is perfectly level with the body of the Tessarisis. Whereas all the other wheels are definitely spring-loaded (you can push them down), this one was different - it would spin, but if you put pressure on it and spin it, you wouldn't feel any kind of clicking due to the ball-bearing mechanism (same on on the Isis rings) not engaging. And how I got it out - I could lift the wheel slightly with my fingernail, and turning it upside down and hitting it slightly with my hand, it falls out. From the looks of it, the mechanism is such that once the wheel goes it, it's virtually impossible to disassemble, as it would lock in good.
I did get an email back from Sonic, and it does appear that it wasn't initially locked in during assembly. Their suggestion was to put a piece of wood on it and strike it to lock it in. If that doesn't work, I need to send it back in for repair. On the plus side, I do have another one coming my way at some point (hopefully soon), but it did really confuse the hell out of me because I've been at it for several days trying to figure out why the thing won't open even after I seemingly have it doing what the clues say it should do.

Fixed it! Took the end of a wooden spoon, ala Sonic's suggestion, and after about five whacks, it seated properly. Now I just have to retrace all my steps to try to resolve the thing (it's an incredibly frustrating puzzle as it is, but more so when it doesn't have all the wheels working)